Devices are known which use resistive and/or capacitive dividers for voltage measurement and/or for protection purposes. Such devices, which operate at medium or at high voltage levels, may be exposed to a strong electric field which, being placed at very close vicinity, may influence measured quantities mainly in case of low-power outputs or introduce high dielectric stress on insulating material or on surface of such an equipment. Further influences can be observed, in case of outdoor installations, during rain or humid conditions, which may change electric field distribution, thus causing error to measured voltage level or causing corona on the surface of the devices or increased partial discharge level within the devices.
A voltage divider can include an insulating body, which can house high voltage impedance being connected to high voltage at one end and to low voltage impedance at the other end. Low-voltage impedance should be connected to the ground. Output of such impedance divider can be done by means of two wires and/or a cable.
Such measurement means can include higher susceptibility to parasitic capacitances and changes to the accuracy of measured voltage, which can provide inaccurate values for protection and/or measurement purposes.
The majority of known voltage sensors use special shielding electrodes, which can be designed for a particular application and for a voltage sensing size and principle use. A general impedance divider can have an insulating body accommodating impedance, which can be connected at one end to high voltage and at the other end to low-voltage impedance. Both high-voltage impedance and low-voltage impedance can form a voltage divider with given division ratio. The voltage divider can be grounded through ground connection. Output wires go through the cable, which can be shielded in order to minimize effects of external field on low-voltage signal going through the output wires. In order to reduce capacitive pick-up from external voltage sources or fields, shielding electrodes can be used around the divider.
Apart from external influences, shielding electrodes improve electric field distribution on surface of the insulating body or within that insulating body, thus enables higher dielectric withstanding of the device.
The use of shielding electrodes can minimize the sensitivity of the voltage divider towards external connections to a high-voltage terminal or to other surrounding devices connected to a high voltage potential.